A device of this kind is described in German Patent No. DE 42 23 813 C1. However the device taught in this patent employs spindles with uniform threads over the whole length of each spindle for dispensing disks from an arrangement of parallel piles of disks. The construction of the spindle is considered a shortcoming of the device for carrying out the function of releasing and feeding discs (disc-shaped elements) from one pile of the parallel mounted piles to another. This shortcoming is attributable to the movement of the spindles which are highly non-uniform, and similar to the movement of a film in a projector. The discs in one pile are withdrawn by a manipulator one disk at a time with the foremost disc transported from a given one pile to an adjacent pile which is moved by one position to provide room for the next disc. The feeding pile is moved again by one position and the manipulator moved back to permit movement of the next disc and so on, until a desired disc for release to a player is at the foremost position.
It is evident that a compromise is being made between the wish to store as many discs as possible in a given space and the need to cope with the tolerances of the discs (and the spindles). Furthermore, in the above cited patent two threaded spindles having a left and right thread orientation rotate in opposite directions which further complicates the operation.
The kernel of the present invention resides in a spindle construction which is applicable to a one or two pile model of disks arranged in tandem so that the spindle is arranged to feed and release the discs from the piles to optimize storage and feeding. This is accomplished in accordance with the present invention by making the thread pitch and diameter of the thread of the spindles narrow in one region where the discs are intended only to be stored, and wider in another region where the discs are intended to move. The change of the thread pitch and diameter is done gradually from opposite ends of the spindle for use in the two-pile model and from the center for the single-pile model. For example, when using standard CD's "(compact discs") of thickness 1.2 mm a tolerance of 40% in thickness of the critical outer rim region is allowable for a number of up to 300 CD's in a single pile of 600 mm length (standard rack depth). In a two-pile model the movements are even more linearized and errors during feeding and releasing are mostly removed.
The construction of the device of the present invention is simplified by using a separate motor for each pile of disks with independent position sensors and using the same spindle construction on both sides i.e. same orientation of threads for the two-pile model arrangement of disks. The allowed tolerances of the disk elements, of for example audio CD's, each having an outer diameter of 120 mm.+-.0.3 mm and a thickness of 1.2 (+0.3/-0.1) mm will dictate the form of the spindles. According to the invention, when the disk elements are CD's, the thread pitch of the spindles in case of a single-pile model will vary in the center region of the spindle whereas in the case of a two-pile model the thread pitch will vary from 3 mm (+0.3) at the opposite ends with the height of the threads varying over the valley of 1.5 mm (.+-.0.2).